The \(K^+\rightarrow \mu ^+\nu X\)  process is investigated in the framework of the scalar and vector mediator models, defined for non-zero mediator mass \(m_X\)  [1]}.
In total, 37 mass hypotheses equally spaced in the range 10–370 MeV/\(c^2\)  are examined. The \(K^+\rightarrow \mu ^+\nu \nu \bar{\nu }\)  decay is investigated assuming the SM differential decay rate distribution [2]}.
